Following the global blooming in mobile communications, various kinds of handheld communication products have been demanded by wireless users. One of the major demands is to minimize the product dimensions. Generally speaking, the dimensions of a communication product can be effectively minimized by using an embedded antenna inside the communication product. However, in the existing communication products, especially those with an embedded antenna, the internal spacing for antenna is usually very limited. Thus, with this spacing limitation, how to achieve good antenna performances and good electromagnetic compatibility with nearby electronic components inside the product has become one of the major design challenges for the final communication product.
For conventional planar inverted-F antennas (PIFAs) applied to mobile phone antennas, the antenna's radiating metal plate is usually horizontally installed above the top portion of the ground plane. A feeding metal pin and a shorting metal pin are electrically connected to and perpendicular to both the radiating metal plate and the ground plane.
A ROC patent publication No. 519780, “Dual-Band and Multi-Band Planar Inverted-F Antenna and the Radiating Metal Plate,” disclosed a planar inverted-F mobile phone antenna This mobile phone antenna comprises one radiating metal plate, one metal ground plane, and one feeding metal line and one shorting metal pin, which are installed perpendicularly to the radiating metal plate and the ground plane. By meandering the resonant path of the radiating metal plate to achieve dual-band operation, the size of the antenna profile can thus be minimized. The drawback of this conventional antenna design, however, is that the antenna is not easy to be integrated with other circuitry systems and associated components. This conventional antenna also requires an isolation distance from the shielding metal box of the radio frequency (RF) circuitry and RF components to reduce the destructive coupling effects on the antenna performances.
FIG. 1A shows a schematic view of a conventional mobile phone antenna with a shielding metal box 15. The antenna element for this mobile phone antenna is a conventional planar inverted-F antenna and mainly comprises one metal plate 11, one feeding metal pin 12, one shoring metal pin 13, and one ground plane 14. The feeding metal pin 12 and the shorting metal pin 13 are both perpendicular to and in between the metal plate 11 and the ground plane 14. The metal plate 11 is mainly parallel to the ground plane 14. The shielding metal box 15 is affixed to and electrically connected to the ground plane 14. Referring to FIG. 1A, the shielding metal box 15 is away from the metal plate 11 with an isolation distance d.
FIG. 1B, shows the measured return loss for the mobile phone antenna in FIG. 1A. The vertical axis represents the return loss in dB; the horizontal axis represents the operating frequencies. As shown in FIG. 1B, the measured return loss for the mobile phone antenna without a shielding metal box 15 is represented by the curve 16. The corresponding operating bandwidth, determined by 2:1 Voltage Standing-Wave Ratio (VSWR) or about 9.6 dB return loss, can cover the Universal Mobile Telecommunication System (UMTS) band. The drawback of this conventional mobile phone antenna is that with a decrease in d (that is, by moving the shielding metal box 15 close to the metal plate 11), the corresponding operating bandwidth is quickly degraded and thus can not cover the required UMTS band.
Referring to FIG. 1B, curve 161 represents the measured antenna return loss when the isolation distance d is 21 mm, while curve 162 represents the measured antenna return loss when the isolation distance d is reduced to 7 mm. To cover the UMTS band, the isolation distance d between the shielding metal box 15 and the metal plate 11 is usually required to be greater than 7 mm such that the antenna performances will not be degraded due to the coupling effects between the antenna and the shielding metal box 15. With this design configuration, the internal spacing utilization and design flexibility have become limited for this type of conventional mobile phone antenna